Stereophonographic apparatus and method



Jul 19, 1938. L DOUDEN 2,124,030

STEREOPHONOGRAPHIC APPARATUS AND METHOD Filed Dec. 31, 1934 5Sheets-Sheet l [:k EII INVENTOR W/LL/AM A. DUUDf/V ATTORNEY July19,1938. w. DOUDEN Filed Dec. 31, 1934 5 Sheets-Sheet 2 INVENTORmama/Z0005 BY ATTORNEY July 19, 1938.

W. L. DOUDEN STEREOPHONOGRAPHIC APPARATUS AND METHOD Filed Dec. 51, 19343 Sheets-Sheet 3 INVENTOR W/l. L/AM L. 00005 ATTORNEY section of thesound reproducing apparatus,

Patented July 19, 1938 STEREO-PHONOGRAPHIC APPARATUS AND METHOD WilliamL. Douden, New York, N; Y., assignor to Radio Corporation of America, acorporation of Delaware Application December 31, 1934, Serial No.759,854

plifiers 3 and 4 of conventional type which serve to amplify theelectrical impulses received from the microphones. The amplifiers 3 and4 are connected to the usual mixer and power amplifier indicated at 5,which may be of any usual commercial type, and the acousticallymodulated electrical output from the amplifier 5 actuates' thegalvanometer B in the known manner used in variable width soundrecording, and is described and claimed in Kellogg Patent 1,740,406.

Connected to the output from the amplifiers 3 and 4 are rectifyingamplifiers 6- and l which provide a direct currentoutput correspondingto the envelope of the audio frequency input to each of the microphones.These amplifiers may be constructed, for example, as shown and describedin MacDowell Patent 1,855,197.

The output from the amplifiers 6 and 'l is fed to solenoids 8 and 9which operate upon cores NJ and I I connected to the mask I2. It will beapparent that if the currents through the solenoid's 8 and9 are equal,the mask l2 will remain stationary in midposition while variations inthe currents through the solenoids 8 and 9 will shift the mask l2laterally by a corresponding amount.

The optical system used is of any convenient commercial type such, forexample, as that shown in the Kellogg patent above referred to, andconsists of an exciter lamp 13 from which the light is condensed on themask [2 by the condenser lens M. An optical system i5 is providedtogether with a lens It for condensing the light upon the mirror of thegalvanometer 6 which vibrates about a horizontal axis, and an additionaloptical system I! is provided which; together with [5 and I6, images theaperture in the member [2 upon the slit member I8 as indi-'- cated at19. An additional lens 20'is provided between the slit member I 8 andthe film 2| for imaging the slit 22 in the member I8 upon the film.

It will be apparent from the foregoing that sound impressed on themicrophones l or 2, or both, is converted into electrical impulses whichvibrate the mirror of the galvanometer fi about a' horizontal axis,thereby moving the triangular image l9 over the slit 22 and illuminatingcorrespondingly varying lengths of the slit;' and this varyingillumination is imaged upon the film- Zl by the lens 20 therebyproducing a variable width sound record of the type havingmodulationabout both sides of an axis.

If the sound input is entirely to the microphone I, it will beapparent'that theramplifieri'l will give a correspondingly difierentcurrent 9 Claims.

This invention relates to an apparatus for so recording and reproducingsound that the listener can tell the direction of origin of the sound,and involves both a new apparatus and a new method for accomplishingsaid result. Heretofore there have been attempts tostereophonographically reproduce sound by the use of two or moresoundtracks or sound records operating corresponding sound reproducers,and in some instances the procedure has been successful but has neverbeen commercially adopted due to the great expense involved in themultiple sound records and the multiple recording and reproducingequipment. The present invention involves such sound recording andreproduction with a single record, and I efiect the shifting of theapparent point of sound reproduction by a shifting of the axis ofrecording in relation to the axis of the soundtrack.

One object of the invention is to provide a method and apparatus forstereophonographically recording sound.

Another object of the invention is to provide a method and apparatus forstereophonographically reproducing sound.

Another object of the invention is to provide a novel photographic soundreproducer.

Another object of the invention is to provide an improved soundrecorder.

Another object of the invention is to provide a sound record which maybe reproduced either stereophonographically on the apparatus for suchpurpose or on a standard sound reproducer.

Another object of the invention is to provide a stereophonographic soundrecord occupying the minimum practical space.

Other and incidental objects of the invention will be apparent to thoseskilled in the art from a reading of the following specification and aninspection of the accompanying drawings, in which:

Fig. 1 is a diagrammatic illustration of my sound recording apparatus.

Fig. 2 is a diagrammatic illustration partly in Fig. 3 is anillustration of the soundtrack.

Fig. 4 is an illustration of a special form of galvanometer for use inmy apparatus, and

Fig. 5 is an illustration of a second form of galvanometer.

Referring first to Fig. 1: l and 2 indicate microphones located at theouter limits. of the sound recording stage. These microphones may be ofany convenient type capable of giving'high quality response, andareconnected to the ammicrophone than to the other, the member I2 will beshifted a proportionate amount. This, obviously, will shift the image l9longitudinally of a slit 22 and will shift the axis of the sound recordin relation to the soundtrack 2| on the film. The position of the soundrecord in relation to the soundtrack area will accordingly indicate theposition of the speaker in relation to the microphones.

The soundtrack produced by Fig. 1 is shown in Fig. 3 where 2| indicatesthe film and 25 indicates the sound record. It will be apparent that inthis case the source of sound moved from near one microphone toward theother and became slightly louder as it approached the second microphoneas is indicated by the movement of the sound record from one side of thesoundtrack to the other and with slightly increased modulation.

In order to reproduce the sound so that it will appear to come from thedirection or position of its original source, I use the apparatus shownin Fig. 2. In this apparatus, an exciter lamp 313 and condenser lens 3|,a slit member 32 and an objective lens 33, all as customary incommercial sound reproducers are used to produce a brilliantlyilluminated image of the slit 32 upon the film 2| in the form of a.narrow line of light. Light passing through the film 2| is directed bythe lens 34 to the reflector 35. This reflector is coated with a layerof silver 36, 31 of varying thickness, being sufiiciently thick at 36 togive complete reflection of the light and tapering to substantially noreflection and complete transmission at 31, and with 50% reflection and.50% transmission at its mid-point. Any equivalent type of reflector may,of course, be used provided it has complete transmission at one edge andcomplete reflection at the other edge with a gradually varyingreflection and transmission between. The mirror reflects light to thelens 38 Which collects it upon the photocell 39, while light transmittedby the mirror 35 is collected by the lens 40 upon the photocell 4|. Thephotocells 39 and 4| actuate amplifiers of any usual commercial typeindicated at 42 and 43 which in turn operate the loudspeakers 44 and 45located in substantially the same relative positions on the stage aswere occupied by the microphones and 2.

It will be apparent that this apparatus will reproduce an ordinary soundrecord having the variable density type or a sound record of thevariable area type having the modulation equally about the middle axisof the soundtrack in the usual manner, the sound being equallyreproduced by the loudspeakers 44 and 45. If, however, a soundtrack ofthe type shown in Fig. 3 is reproduced in the apparatus when thesoundtrack is imaged primarily upon the portion 31 of the mirror, thelight will be substantially transmitted thereby and will be focussedupon the photocell 4|, thereby actuating only the loudspeaker 44 andcausing the sound to come from the corresponding side of the stage. Asthe soundtrack reaches mid-position, half of the light will reach thephotocell 4| and the other half will reach the photocell 39, therebyequally actuating the loudspeakers 44 and 45, and causing the sound toappear to come from the middle of the stage; while when the soundtrackimage is adjacent the point 36 of the mirror 35 substantially all thelight will be reflected to the photocell 39 and cause the sound toappear to come from the other loudspeaker 45.

It will be apparent that with this arrangement I can use modulationthrough either recording amplifier amounting to the full capacity of thesoundtrack as when the axis of the sound record is shifted to coincidewith one side of the soundtrack the modulationbecomes of the single orsaw-tooth type and may extend over the entire width of the soundtrack.The one loudspeaker reproducing all the sound from one half of thesoundtrack and the other loudspeaker which reproduces the sound from theedge of the track opposite to the axis of the record reproducing thepeaks of the modulation and thereby giving good quality soundreproduction.

Instead of using the movable diaphragm I2 and the galvanometer 6 asshown in Fig. 1, I may use a galvanometer such, for example, as thatshown in Egerton Patent 1,605,930 in which the mirror is capable ofmovement about two perpendicular axes, but I prefer to use agalvanometer of the type shown in Fig. 4. In this galvanometer,indicates a metallic frame mounted pivotally on a vertical axis on thepivots SI and 62. This frame carries two independent coils 63 and 64which are respectively connected to the amplifiers 6 and of Fig. 1, andthis entire assembly is mounted between the pole-pieces 65 and 66between which there is an appropriate magnetic field. It will beapparent that any lack of balance in the current through the coils 63and 64 will evidence itself as a corresponding movement of the frame 60in one direction or the other. Mounted within the frame 60 onappropriate pivots 6'! and 68 is a shaft 69 carrying a mirror 10. Tothis mirror is connected a driving rod H which serves to vibrate themirror about a horizontal axis in response to audio frequency currents.ing rod H by a vibrating reed 13 of an appropriate. driving motor such,for example, as that shown in Dimmick Patent 1,936,833. The driving rod1| is reduced in thickness at 12, as indicated, to permit it to flexabout the vertical axis defined by the pivots 6| and 62. It will beapparent that in this construction the mirror 10 will be capable ofrapid vibrations about the horizontal axis in response to audiofrequencies while the frame 60, which would not readily oscillate atsuch high frequencies, follows the movement of the source of sound.

In the form of galvanometer shown in Fig. 5, the unit is a completegalvanometer of the type shown and described in Dimmick Patent1,936,833, and is mounted to pivot about a vertical axis on the pivots8| and 82. An appropriate arm 83 is connected to the pivot 82 for thepurpose of moving the galvanometer about the vertical axis about whichit is maintained in approximate position by the spring 83. Solenoids 84and 85 actuate the tension members 86 and 81 which are connected toopposite ends of the member 83, and thereby serve to move thegalvanometer about a vertical axis. The solenoids 84 and 85 areconnected to the amplifiers 6 and I, while galvanometer 8!! is connectedto the amplifier 5 in the same manner as the galvanometer 6.

It will be apparent that in conjunction with The modulation is suppliedto the drivmy apparatus I may also use a ground-noise reduction systemof the same general nature as shown in the MacDowell patent. abovereferred to, and connected to the mask 12 to shift it vertically in themanner shown, described, and claimed in Maurer application Serial No.602,135, filed March 31, 1932 and Kellogg application Serial No.621,787, filed July 11, 1932. In such case, of course, the ground-noisereduction apparatus would be connected to the output of the amplifier 5in the manner there described.

Likewise, I may use the ground-noise reduction system of either RobinsonPatent 1,854,159, or Hewlett Patent 1,853,812, or Hanna Patent1,888,724, in which case the ground-noise reduction amplifier will beconnected to the galvanometer 6, the vibrating means for the reed 12 orthe galvanometer Bil, so as to shift the spot of light l9 vertically inrelation to the slit 22.

Having now described my invention, I claim:

1. Sound reproducing apparatus comprising means for illuminating aphotographic soundtrack, a plurality of photocells and a, mirror fordirecting light passing through said soundtrack to said photocells, oneedge of the surface of said mirror being substantially completelyreflecting for directing said lights to one of said photocells and theother edge of said mirror surface being substantially completelytransparent for transmitting said light to another of said photocells.

2. In the method of sound recording which comprises the imaging upon afilm of an illuminated portion of a slit which is illuminated by theimage of a triangular aperture, the steps of vibrating said triangularimage transversely of said slit in accordance with the acousticvibrations to be recorded, and shifting the image longitudinally of theslit in accordance with the position of the acoustic vibrations to berecorded.

3. In the method of sound recording which comprises the imaging upon afilm of an illuminated portion of a slit which is illuminated by theimage of a triangular aperture, the steps of vibrating said triangularimage transversely of said slit in accordance with the acousticvibrations to be recorded, shifting the image longitudinally of the slitin accordance with the position of the acoustic vibrations to berecorded, and shifting the mean position of said image transversely ofthe slit in accordance with the average amplitude of the vibrations tobe recorded.

4. Sound reproducing apparatus comprising means for illuminating a soundtrack varying in transparency along its length, a plurality ofphotocells, a mirror for directing light passing through said soundtrack to said photocells, one edge of the surface of said mirror beingsubstantially completely reflecting and the other edge of the surface ofsaid mirror being substantially completely transparent, amplifiersconnected to said photocells and loudspeakers connected to saidamplifiers, whereby the amplitude of response from each of the speakersis determined by the position of the sound recorded laterally of thesound track.

5. Sound reproducing apparatus comprising means for illuminating a soundtrack varying in transparency along its length, a plurality ofphotocells, a mirror for directing light passing through said soundtrack to said photocells, one edge of the surface of said mirror beingsubstantially completely reflecting and the other edge of the surface ofsaid mirror being substantially completely transparent, amplifiersconnected to saidphotocells, loudspeakers connected to said amplifiers,a sound record having its axis shifted in proportion to the position ofthe sound recorded thereon between said illuminating means and saidmirror whereby the response of each of the loudspeakers is determined bythe position of the said sound track.

6. Sound reproducing apparatus comprising means for illuminating a soundtrack varying in transparency along its length, a plurality ofphotocells, means for directing light passing through said sound tracksimultaneously to said photocells in a ratio of illumination determinedby the position of the illumination on said directing means, amplifiersconnected to said photocells and loudspeakers connected to saidamplifiers, whereby the amplitude of response from each of the speakersis determined by the position of the sound recorded laterally of thesound track.

7. Sound reproducing apparatus comprising means for illuminating a soundtrack varying in transparency along its length, a plurality ofphotocells, means for directing light passing through said sound tracksimultaneously to said photocells in a ratio of illumination determinedby the position of the illumination on said directing means, amplifiersconnected to said photocells, loudspeakers connected to said amplifiers,a sound record having its axis shifted in proportion to the position ofthe sound recorded thereon between said illuminating means and saiddirecting means whereby the response of each of the loudspeakers isdetermined by the position of the said sound track.

8. Sound reproducing apparatus comprising means for illuminating aphotographic soundtrack, a plurality of photocells and a mirror fordirecting light passing through said soundtrack to said photocells, oneedge of the surface of said mirror being substantially completelyreflecting for directing said light to one of said photocells and theother edge of said mirror surface being substantially completelytransparent for directing said light to another of said photocells, thepro-portion of light reflected to that transmitted varying uniformlybetween the said two edges.

9. Apparatus of the classdescribed including two photocells, meansdirecting a beam of light toward said photocells and a mirror fordirecting light from said beam to said photocells, one edge of thesurface of said mirror being substantially completely reflecting fordirecting said light to one of said photocells and the other edge of thesurface of the mirror being substantially completely transparent fordirecting said light to another of said photocells, the ratio ofreflection and transmission being graduated between said edges.

WILLIAM L. DOUDEN.

